The invention relates to a method for the spatially resolved introduction of an intensity pattern comprising electro-magnetic radiation into a photosensitive substance with properties, which can be changed by photon radiation, as well as a device for implementing such a method. The present invention can particularly be used for writing, deleting, and rewriting an optic data carrier as well as for the formation of micro and nano-scaled structures. These applications and/or utilizations are included in the scope of the present invention.
The photosensitive substance used within the scope of the present invention shows as the initial status a first, liquid state and can change its properties by photon radiation into at least a second state. The change of this feature occurs such that electro-magnetic radiation is guided via an optic display system into the substance and is here projected on predetermined spatial coordinates, in order to create a change of the properties of the substance at these spatial coordinates and/or areas surrounding these spatial coordinates. The electro-magnetic radiation may particularly represent a collimated laser beam, without generally being limited thereto, which is projected by the optic display system on a volume with limited diffraction, thus in a focused fashion. The changes of the properties of the substance may be lasting, and for example represent a change of the liquid state into a solid one; for applications such as data storage the variation of the properties of the substance may also be only temporary and for example can be reversed by a thermal treatment of the substance or reverse automatically. For the rest, even a lasting change may be either reversible or non-reversible.
Within the scope of the present invention the first, liquid state of the photosensitive substance used shall not be understood exclusively as a liquid state, thus as the status of a substance in which it provides hardly any resistance to a change of shape and/or in case of a thickly-viscous fluid only a slight resistance, however poses a rather strong resistance to a change of volume, but the photosensitive substance may be present in its first, liquid state also as a paste, thus a mixture of solid and liquid matters, or a suspension with a high content of solid matter, which perhaps is no longer flowing or spreadable at all.
The electro-magnetic radiation used within the scope of the present invention usually represents light in the visible or infrared spectrum. When in the following for reasons of a simplified illustration and/or wording only “light beam”, “light irradiation”, or “exposure” is used, this shall be understood only as examples and does not exclude that perhaps also electro-magnetic radiation of other wavelengths can be used within the scope of the present invention.
Within the scope of the present invention the spatially resolved introduction of the electro-magnetic radiation occurs by an optic display, with the radiation being projected as an intensity pattern, particularly in a focused fashion. When in the following the term “focusing” is used, this represents an example for the introduction of optically projected intensity patterns of the electro-magnetic radiation into the photosensitive substance, because within the scope of the present invention projection of other intensity patterns may also be used in the image plane within the photosensitive substance.
A method and a device of the present type are generally used for the spatially resolved exposure (in the following also: writing) of one, two, or three-dimensional structures in the photosensitive substance, in order to particularly store data in a multi-dimensional fashion or to create multi-dimensional objects and/or structures and masks in the scale of nanometers and micrometers.
In the field of stereo-lithography for the creation of structures in the macro-range, for example, it was suggested in DE 101 11 422 A1 to introduce a light beam into a liquid photosensitive substance and to focus it here, so that the substance transformed from its liquid into a solid state. This change of the properties of the substance occurs in the ideal case precisely in the area of said focus. This may be achieved both by a linear as well as by a non-linear effect: either the substance reacts linearly, but shows an intensity limit, below which any change by irradiation cannot occur or only to an insufficient extent, or the substance reacts in a non-linear fashion, which is particularly the case in two or multi-photon polymerization. In the latter method the probability for changing properties of the substance in the focus is amplified by the here increased intensity in reference to the environment.
The precise, spatially resolved introduction of a focused light beam into a photosensitive substance is particularly suitable for the production of a three-dimensional structure when the change of the substance is caused relatively precisely and exclusively in the focus. Because due to suitable display systems, for example Piezo-lifts, for moving the substrate or the beam deflecting devices, such as galvanoscope, micro-mirror actuators, spatial modulators for light, or acousto-optic deflectors the focus can range over a relatively large, three-dimensionally extended writing area in the photosensitive substance. This is rather irrelevant for stereo-lithographic methods, such as the one known from DE 101 11 422 A1, but is interesting particularly for the production of nano and micro-scaled structures, light wave conductors, or spatially disbursed, writable optic data storage units, in which a primary aspect is given to the high resolution of the structures and thus objective lenses must be used in connection with immersion means. In order to overcome the diffraction limit here, which depends on the wavelength of the light used and the Abbe limit, it has been suggested in EP 1 616 344 B1 to incite the spatially resolved changes of the properties of the substance by a diffraction-limited signal and to simultaneously and spatially cancel this change using an off-set diffraction limited signal.
In case of a change of the spatial coordinates along the optic axis of the optic display system used the problem develops however, like everywhere in the field of displaying optics, that display errors or aberrations occur, with their number growing with increased writing depth, thus with an increasing portion of material in the optic path not optimally adjusted to the diffraction index. Therefore, in prior art three-dimensional structures can be created with an only very limited height.
A method is already known for the field of two and multi-photon absorption lithography, which attempts to statically compensate the problem of display errors by utilizing preliminary compensation. In the publication APPLIED OPTICS, volume 27, number 26 (1998), a method is described, which uses two tubular lenses, which can be displaced along the optic axis. By a relative displacement of the tubular lenses aberrations of all orders are created, which can be selected such that they partially compensate particularly the errors of the subsequent optic system. This method allows an only partial compensation of aberrations and is technically extremely complicated, because additional components are used, which in turn are subject to errors and must be moved. Additionally, for each irradiation level along the optic axis a new relative position of the tubular lenses must be adjusted. Furthermore, due to the use of the tubular lenses the display shifts along the optic axis such that the compensated display is extended or compressed. Under certain circumstances, additionally the irradiated dosage of light may be changed in the compensated display, which has disadvantageous effects upon the resulting structures.